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(1980)Journal ArticleThe category theory concept of a commutative diagram is used to construct a model of the way in which symbolic processes are applied to problem solving. The model provides for a relationship between symbolic processes and the problem which depends on structural isomorphism and consistency, but is independent of similarity between symbol elements and problem elements. It is then shown that several different levels of thought can be distinguished within the basic model. More information is needed to assign symbolic processes to a problem in a consistent way with higher-level thought processes than with lower-level processes. These information-processing requirements permit the approximate age of mastery of each level to be predicted, thereby offering an alternate theory of cognitive developmental stages. Two experiments designed to test the theory are reported.
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(1989)ReportAnalysis of pipe tests to determine friction coefficients and their uncertainty is discussed. Optimisation methods are applied to finding the pipe diameter, friction coefficient and fitting loss coefficient from a pipe test. A FORTRAN program implementing these methods is included.
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(1989)ReportDescribes an investigation into the mechanisms responsible for sludge carry-over during decant from intermittent aeration tanks. Several mechanisms were identified which may cause sludge carry-over. An "early failure" mode may occur during the transient phase at the start of decant. This can be avoided by gradually increasing the rate of decant to a final steady value. The time required for flow establishment is in the order of five minutes in tanks of current size. Following the transient phase, failure can occur when interfacial shear stresses between the supernatant and settled sludge exceed some critical value. This is considered to be a "scour failure" analagous to the onset of erosion of a cohesive sediment. Experiments conducted in a variety of different types of extended aeration tanks indicated that the critical parameters governing failure are the upstream velocity of the supernatant, the settlement time, and the Stirred Sludge Volume Index, SSVI. Appreciation of the failure mechanisms has indicated certain design improvements which could be made to existing aeration tanks, in particular to the rate of changee of weir loading and the design of scum barriers. The significance of tank depth is also discussed.
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(1989)ThesisIn this project the preparation of the electrolyte for the all vanadium redox flow battery was investigated using both chemical and electrolytic reduction of ^O,- powder. Oxalic acid and SO^ reduction were found to be unsuitable as only the V(IV) state could be produced directly. With suspended powder hydrolysis, however, vanadium sulphate of any oxidation state, in this case 50% V(IV) plus 50% V(III) in sulphuric acid can readily be prepared from V^O^ powder, thus allowing a significant reduction in the cost of the vanadium battery electrolyte. Results from conductivity and electrolyte stability tests at elevated temperature have led to modification of the electrolyte composition for the vanadium redox cell, from the 2 M V plus 2 M H^SO^, originally employed, to the use of 3 M H^SO^, much higher energy efficiencies and greater electrolyte stability was demonstrated with the 3 M H^SO^ supporting electrolyte. Spectroscopy and electrolyte conductivity have been demonstrated as suitable techniques for state-of-charge monitoring. A number of electrode materials were also evaluated and a Toray graphite bonded to a carbon plastic electrode was selected for further prototype development. Energy efficiencies of between 83 and 86% were obtained for a current density of 30 mA/cm for a temperature range 5 to 45'C, and between 0 and 100% state-of-charge. A wide range of construction materials was tested for long term stability in the vanadium redox electrolyte.